I recently did this the hard way myself. Searching back through the thread it was pointed out you can more or less cheat using the Traveller's Belt item to transfer materials to/from the spirit realm. I took it as a personal challenge to do it a harder way. My goal was to build an ender chest in both worlds. Obsidian was easy using copper to make a mariculture vat with water/lava in. The hard part is reaching an eye of ender. Ender pearls themselves can come from oyster pearls you can cultivate (and alter essence of ender seeds you make).
The blaze powder is the really tough part: this needed a blaze seed. For that I started from scratch in the spirit world getting garden soil, basic botania for an altar and then going back and doing those repeatable quests that give you copper/iron/etc essence and then making new essence seeds. Finally working my way up to an infusion stone to make regular essence. One final thing that nearly stumped me was how to make a fire rune as it appeared there is no source of nether wart in the spirit world. The solution is that just like wispy cotton moves between worlds so does Mutandis. So make a ton of it back in the overworld and then play mutation roullete on plants in the spirit world and eventually you will get nether wart.
Good luck! It's rewarding doing it the hard way, or if you can't be bothered you can 'exploit' the Traveller's Belt.
Oh one more hint: to get all the floral powder you need for the repeatable essence quests you'll need floral fertalizer which needs bone meal. Either come back to the dream world during a nightmare to kill skeletons. Or use a manasteel shovel on ancient and on the ocean bottom and it can drop bonemeal/bones.
Ok, how did you get past the iron thing?